1. Field of the Invention
One embodiment of the present invention relates to an imaging device including an oxide semiconductor.
Note that one embodiment of the present invention is not limited to the above technical field. Specifically, examples of the technical field of one embodiment of the present invention disclosed in this specification include a semiconductor device, a display device, a method for driving any of them, and a method for manufacturing any of them.
In this specification and the like, a semiconductor device generally means a device that can function by utilizing semiconductor characteristics. A transistor and a semiconductor circuit are embodiments of semiconductor devices. A storage device, a display device, an imaging device, or an electronic appliance includes a semiconductor device.
2. Description of the Related Art
A technique to form transistors by using semiconductor thin films formed over a substrate having an insulating surface has been attracting attention. The transistor is used in a wide range of electronic devices such as an integrated circuit (IC) or an image display device (also simply referred to as a display device). As semiconductor thin films applicable to the transistors, silicon-based semiconductor materials have been widely used, and oxide semiconductors have been attracting attention as alternative materials.
For example, a technique for forming a transistor using zinc oxide or an In—Ga—Zn-based oxide semiconductor as an oxide semiconductor is disclosed (see Patent Documents 1 and 2).
Patent Document 3 discloses that a transistor including an oxide semiconductor and having an extremely low off-state current is used in at least part of a pixel circuit and a transistor including a silicon semiconductor with which a complementary metal oxide semiconductor (CMOS) circuit can be formed is used in a peripheral circuit, whereby an imaging device with high speed operation and low power consumption can be manufactured.